1. Field of the Invention
The present invention relates to a lift assist type mechanism for use with heavy tools which require manual lifting, for example rotary drills for making holes in the ground, or demolition tools such as jackhammers or rock drills for breaking pavement and the like.
2. Description of the Related Art
Jackhammers are demolition tools commonly used in the construction industry for breaking up pavement such as concrete sidewalks, asphalt roadways, and similar types of working surfaces. Typically, jackhammers are pneumatically driven and have a chisel or other type cutting tool which is repeatedly hammered into the working surface with a reciprocating motion.
Jackhammers can typically weigh as much as 90 pounds. The force required to lift the jackhammer out of a hole can be as high as 300 or more pounds because of the resistance encountered in removing the drill bit from the rubble. Workmen operators performing pavement demolition are generally required to lift the jackhammer to reposition it after completing each portion of the work. Such repeated lifting causes severe stress on the musculoskeletal structure of the human body, resulting in repetitive strain injuries of the shoulders, back, legs, and other parts of the body, which are occupational hazards for such machinery operators. These injuries are painful, and time consuming to treat, with the resultant costs connected with such injuries involving not only the medical cost for treatment, but also down time while the operator recovers.
Lift assist devices for jackhammers are known. For example, U.S. Pat. No. 2,622,562 to Longenecker discloses a detachable lifting jack for fluid actuated tools of the percussive type, such as pavement breakers. The lifting jack includes two telescoping elements: a first one being rigidly affixed to the portable cutting machine, and the second one being slidably connected to the first one and adapted to engage the working surface. Fluid pressure applied to the second element applies force to the working surface which lifts the cutting machine.
U.S. Pat. No. 4,548,279 to Zaruba discloses a demolition tool provided with an extractor for removing the chisel or drill bit from the working surface. The extractor is a piston equipped with a foot which maintains contact with the working surface. When the tool is to be extracted the piston is actuated to press down upon the working surface thereby causing the chisel or drill bit to be forced upward.
While such prior known devices can achieve lifting of the drilling machinery, they suffer from certain disadvantages. First, the operator is still required to lift the jackhammer to move it from place to place. While it may be possible, for example, to pivot the Longenecker apparatus to "walk" the tool to the next location after the chisel has been extracted from the pavement, lifting is still required to overcome the cutting action of the Longenecker pointed tip and the associated friction between the tip and ground. The same is true for the Zaruba extractor. No means are provided to move the entire apparatus to another location without lifting or dragging it to the next work location.
Second, lifting mechanisms in contact with the working surface are subject to very severe bending forces, especially when the machinery is not held perpendicular to the working surface but angled with respect to the vertical direction as, for example, when the machinery is transported to another location. Simple pneumatic cylinders and telescoping pistons do not have sufficient resistance to bending. Accordingly, a need exists for a lift assist device for a demolition tool which is relatively lightweight, portable, easy to use, and which is cost effective.